1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. In particular, the present invention relates to, for example, a semiconductor device, a display device, a light-emitting device, a power storage device, a driving method thereof, or a manufacturing method thereof. The present invention particularly relates to a semiconductor device, a display device, or a light-emitting device each including an oxide semiconductor, for example.
Note that in this specification, a semiconductor device refers to any device that can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all included in the category of semiconductor devices.
2. Description of the Related Art
In recent years, flat panel displays such as liquid crystal displays (LCDs) are becoming widespread. In each of pixels provided in the row direction and the column direction in a display device such as a flat panel display, a transistor serving as a switching element, a liquid crystal element electrically connected to the transistor, and a capacitor connected to the liquid crystal element in parallel are provided.
As a semiconductor material for forming a semiconductor film of the transistor, a silicon semiconductor such as amorphous silicon or polysilicon (polycrystalline silicon) is generally used.
Metal oxides having semiconductor characteristics (hereinafter referred to as oxide semiconductors) can be used for semiconductor films in transistors. For example, techniques for forming transistors including zinc oxide or an In—Ga—Zn-based oxide semiconductor are disclosed (see Patent Documents 1, 2 and 3).